1. Field of the Invention
The invention relates to apparatus for adjusting the position of an edge between two surface portions having relatively different reflection-coefficient to wavelength relations, both said surface portions extending in a plane of a longitudinally movable belt which is also movable in the plane of its surface in a direction transverse to its longitudinal movement.
2. Description of the Prior Art
A position adjustment of this kind may be useful for widely different technical purposes. For example, frequently it is necessary to apply some treatment along the edge of one of the two surface portions while the belt runs through. In many cases it is also necessary to apply treatment along a pre-drawn line which in its turn mostly has a certain minimum width to be sufficiently clearly perceptible so that in a manner of speaking it represents a surface defined by two edges and having a reflection coefficient which differs from that of the remaining surface. There must be different spectral reflectivities in order that optical detection can be effected. In other words this optical detectability of the difference in the two surfaces represents the basic criterion for the kind of device to which this invention relates.
Control system of the above discussed kind are however no longer feasible where the mutually adjacent surfaces of the belt or strip no longer have a significant size, i.e. where said pre-drawn line has a width of negligible size.